This is a pilot study of inhaled antibiotic regimens is a pilot study examining clinical and laboratory endpoints of patients on inhaled antibiotic treatments. We hypothesize that alternation therapy utilizing Cayston and Tobi will inhibit antibiotic resistance and that alternation therapy will result in a decreased incidence of antibiotic resistance to Cystic Fibrosis (CF) microbial isolates. The long term strategic goal is to develop a model biometric system for selecting a patient's optimal inhaled antibiotic regimen by utilizing clinical and microbiological parameters.